Presence Of Radical Scavengers Research Articles

Degradation of liquid phase N,N-dimethylformamide by dielectric barrier discharge plasma: Mechanism and degradation pathways

The degradation of liquid phase N,N-dimethylformamide (DMF) using the dielectric barrier discharge (DBD) plasma was studied in the present study. The results showed that 1000 mg L−1 DMF could be degraded by DBD plasma under different input power, treatment time and initial pH values of aqueous solution. After 40 min with DBD plasma discharge, 52.2% degradation efficiency was achieved at DMF concentration of 1000 mg L−1 with an input power of 16.19 W under initial pH of 11.14 in aqueous solution, and the energy efficiency of the system was 13.2 mg kJ−1. The removal efficiency decreased with the presence of radical scavenger, manifesting that •OH plays a critical role in the degradation process. The value of TOC in DMF aqueous solution decreased from 790 mg L−1 to 507 mg L−1 in 40 min, which indicated that DBD plasma has the ability to mineralize a portion of DMF in liquid directly. Additionally, the analysis of FTIR, HPLC and the small molecular organic compounds before and after the DBD plasma degradation indicated that the intermediates of DMF in degradation process were N-methylformamide, methanol, formaldehyde and formic acid, which were finally mineralized into ammonia nitrogen, CO2 and H2O. Moreover, the possible degradation mechanism and pathways were proposed.

Photodegradation of ceftriaxone in aqueous solution by using UVC and UVC/H2O2 oxidation processes

This study investigated the performance of UVC/H2O2 and UVC processes for the degradation and mineralization of ceftriaxone as an antibiotic. The highest ceftriaxone degradation was obtained at a solution pH of 5 and H2O2 concentration of 10 mg/L. The apparent rate constant of ceftriaxone degradation was found to be 0.0302, 0.0165, and 0.0065 min−1 in the UVC/H2O2 process for the initial ceftriaxone concentrations of 5, 10, and 20 mg/L, respectively. Degradation and mineralization efficiencies of ceftriaxone was obtained to be 100% and 58%, respectively, in UVC/H2O2 process at reaction time of 120 min, whereas only 61% and 2.5% of ceftriaxone could be degraded and mineralized by UVC. The synergistic effect of UVC/H2O2 was found to be 35%. The presence of anionic species improved the photolysis efficiency which degraded ceftriaxone from 61 to 83%, while, in the UVC/H2O2 process, ability degradation declined from 100 to 70%. The efficiency of UVC/H2O2 and UVC process was not greatly affected in real tap water. Besides, the reduction patterns in the UVC/H2O2 and UVC processes were better described by pseudo-first- and second-order kinetics model with a reaction rate constant of 0.0165 and 0.0012 min−1, respectively. The rate constant of ceftriaxone degradation in the UVC/H2O2 process and at the presence of radical scavenger was found to be around 3.3 times lower than the one in its absence.

Degradation of aniline in aqueous solution by dielectric barrier discharge plasma: Mechanism and degradation pathways

The degradation of aniline solution using the dielectric barrier discharge (DBD) plasma was studied in this paper. The results indicated that the initial concentration of aniline, applied voltage and initial pH value affected the removal efficiency of aniline significantly. After 12 min with DBD plasma treatment, 90.2% removal efficiency was achieved at aniline concentration of 100 mg L−1 with an applied voltage of 3.0 kV and pH 8.43. The removal efficiency decreased with the presence of radical scavengers, indicating that hydroxyl radical plays a key role in the degradation process. The removal efficiency increased obviously when Fe2+ was added. Additionally, the intermediate products generated in the degradation process of aniline were analyzed by some analytical techniques, including total organic carbon analysis, ultraviolet-visible spectroscopy, Fourier Transform Infrared spectroscopy, Gas Chromatography-Mass Spectrometer, etc. The results showed that the degradation of aniline was mainly due to the strong oxidizing capacity of hydroxyl radical produced by the DBD plasma system. Based on the intermediate products identified in the study, the possible degradation mechanism and pathways were proposed.

Aerobic oxidation of alkyl chain in alkylphenols over combination of Pt and Pd catalysts

Oxidation of benzylic position in alkylphenols with molecular oxygen in acidic conditions, which is very difficult because of the intense dimerization or polymerization, was investigated with various combinations of noble metal catalysts. The combination of Pt/C and Pd(CH3COO)2 catalysts showed activity in the formation of p-hydroxybenzaldehyde formation from p-cresol. The best p-hydroxybenzaldehyde yield was 35%, which was obtained in 50 wt% aqueous acetic acid, Pt on carbon : Pd(CH3COO)2 weight ratio = 1 : 2, at 353 K. From XRD, TEM-EDX and XAFS characterizations, the Pt and Pd species were totally reduced to Pt and Pd metal particles, respectively, in spite of the oxidative reaction conditions. Polymerized products (“tar”) of p-cresol formed with Pt/C catalyst and air can be the reductants for Pd(CH3COO)2 into Pd metal. The catalysts or catalyst combinations without Pd metal showed no activity in the formation of p-hydroxybenzaldehyde, suggesting that Pd° is the active species. The effects of the air pressure and presence of radical scavenger were very small, suggesting that non-free-radical mechanism was involved.

Enhanced heterogeneous catalytic oxidation of 2,4-dichlorophenoxyacetic acid in aqueous solution by nanoscale zero-valent iron particle@suparticlelfur/nitrogen dual-doped r-GO (nZVIPs@SN-G) composites

Herein, we reported the synthesis of nanoscale zero-valent iron particles stabilized by sulfur/nitrogen dual-doped r-GO (nZVIPs@SN-G) and their applications as the heterogeneous catalysts to the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by combining H2O2 under varying pHs, temperatures, catalyst dosages and H2O2 concentrations, as well as in the presence of radical scavengers. The experimental results showed that this heterogeneous Fenton-like catalytic system remained effective up to 90 min of reaction time, and could reach at least 98% degradation efficiency at the optimal conditions, especially when the initial pH values were below 4.5. And the scavenging experiments revealed that 2,4-D was mainly decomposed by the attack of surface-bounded hydroxyl radicals (OH). The structure and properties of the nZVIPs@SN-G catalyst was characterized by X-ray diffraction (XRD), scanning elctron microscopy (SEM), surface area analysis (BET), Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS). The SEM images indicated that nanoscale zero-valent iron particles (nZVIPs) with size of about 10–50 nm were uniformly stabilized on the surface of sulfur/nitrogen dual-doped r-GO (SN-G), and had good combination with the multilayer matrix. Additionally, the catalyst at the optimum pH could maintain effective degradation even after five cycles, and achieved 91% degradation efficiency of 2,4-D, which was indicative of a good stability. More importantly, the possible reaction mechanism and dechlorination pathway of 2,4-D by the nZVIPs@SN-G/H2O2 heterogeneous catalytic system was also illustrated in this study.

Novel FeMgO/CNT nano composite as efficient catalyst for phenol removal in ozonation process

A novel FeMgO/carbon nanotube composite (FeMgO/CNT) was synthesised using a chemical vapor deposition (CVD) method and applied to catalytic ozonation for phenol degradation. The degradation performance and mineralisation of phenol in the FeMgO/CNT catalytic ozonation process (COP) were compared with a sole ozonation process (SOP), and various parameters (e.g. presence of radical scavengers, solution pH, ozone dosage, and FeMgO/CNT dosage) were investigated. Phenol degradation during ozonation improved in the presence of the catalyst due to the ability of FeMgO/CNT to decompose ozone and generate hydroxyl radicals. The results indicated that the FeMgO/CNT catalyst promoted the degradation of phenol, Total organic carbon (TOC), higher than 22 and 9% if compared to the SOP (at pH 7, O3: 0.304 g L−1 h−1, 1 g L−1 catalyst) and the catalyst had a high efficiency over a wide pH range. We established an predictive kinetic model of phenol degradation, in which the main factors (i.e. catalyst dosage, ozone concentration, and initial pH) had important effects. Finally, the decrease in phenol removal efficiency of only 8.7% after reusing the catalyst four times illustrates that this catalyst has high stability and can be re-used.

Investigating the aerated VUV/PS process simultaneously generating hydroxyl and sulfate radicals for the oxidation of cyanide in aqueous solution and industrial wastewater

The present study was designed to investigate the cyanide oxidation by the aerated VUV/S2O82- (VUV/PS) advanced process. The effect of persulfate concentration, cyanide concentration, aeration and nitrogen gas blowing in the batch experiments and of hydraulic retention time and presence of radical scavengers in the continuous-flow experiments were investigated. It was found that cyanide oxidation in the aerated VUV/PS process followed a pseudo-first order reaction kinetic. Complete destruction of 50 mg/L cyanide was achieved in the aerated VUV/PS batch process in the presence of 200 mg/L persulfate within the reaction time of 10 min. The scavenging tests indicated that both hydroxyl and sulfate radicals were simultaneously generated in the aerated VUV/PS process contributed in the cyanide oxidation. It was also found that the aeration could enhance performance of the process in oxidation of cyanide due to the generation of ozone. The presence of water anions considerably decreased the cyanide removal efficiency in the aerated VUV/PS process and carbonate had the highest interference. Carbonate, ammonium, and nitrate were the main by-products of cyanide oxidation in the aerated VUV/PS process showing that cyanide was completely oxidized to much less noxious compounds. The complete oxidation of 50 mg/L cyanide in the continuous-flow aerated VUV/PS process at a hydraulic retention time of 20 min indicates the potential of its field-scale application. A real industrial wastewater sample containing high concentration of cyanide, Cr(VI) and organic content was also efficiently treated in the aerated VUV/PS process. Therefore, it is concluded that the aerated VUV/PS process is a promising process for complete destruction of cyanide in industrial wastewater.

Ozonation of Reactive Orange 4 dye aqueous solution using mesoporous Cu/SBA-15 catalytic material

The catalytic ozonation using mesoporous SBA-15 supported copper catalyst (Cu/SBA-15) was employed for the degradation of reactive orange 4 (RO4) azo dye in aqueous solution. The catalyst was synthesized and characterized using BET, SEM, TEM and EDX techniques. The characteristic results revealed highly ordered mesoporous structure, uniform pore sizes, parallel arranged channels and large surface area for the catalyst. The effects of copper loading on SBA-15, initial solution pH and ozone dose on the degradation of RO4 dye were studied. The complete colour removal from RO4 azo dye aqueous solution was obtained after 21 min of ozonation. The maximum TOC removal efficiency of 86% was obtained at optimum operational conditions of 2% copper loadings, initial solution pH 9 and ozone dose of 5 g/m3 after 60 min reaction time. The degradation pathway of catalytic ozonation reaction was studied by adding t-butanol as radical scavenger and it was found that the presence of radical scavenger had no effect on colour removal efficiency suggesting direct ozone molecular type mechanism. However, TOC removal efficiency was significantly reduced with the addition of t-butanol, thereby, indicating a hydroxyl radical based mechanism. The catalytic ozonation reaction followed pseudo-first order kinetics with respect to RO4 dye concentration. The reusability study for the catalyst suggested a negligible loss in the degradation efficiency after five runs of experiments. The stability of the catalyst was studied by performing leaching experiments which suggested that the catalyst has the potential to be utilized for the degradation of aqueous dye solution.

Degradation of 2, 4-dichlorophenol in aqueous solution by dielectric barrier discharge: Effects of plasma-working gases, degradation pathways and toxicity assessment

Chlorinated phenols are a class of contaminants found in water and have been regarded as a great potential risk to environment and human health. It is thus urgent to develop effective techniques to remove chlorinated phenols in wastewater. For this purpose, we employed dielectric barrier discharge (DBD) in this work and studied the efficiency of DBD for the degradation of 2,4-dichlorophenol (2,4-DCP), one of the most typical chlorophenols in the environment. The effects of pH value, applied voltage and plasma-working gases on the dichlorophenol-removal efficiency were investigated. The results demonstrate that DBD plasma could successfully degrade 2,4-DCP, achieving efficiency of 98.16% (k = 1.09 min−1) in the Ar-DBD system, and 77.60% (k = 0.48 min−1) in the N2-DBD system, with the process following the first-order kinetics. The removal efficiency was reduced in the presence of radical scavengers, confirming that hydroxyl radicals played a key role in the degradation process, while other active substances were also found such as nitrogen radicals in the N2-DBD system, which was found to have also contribution to the degradation of 2,4-DCP. The intermediates and final products generated in the degradation process were analyzed using gas chromatography-mass spectrometry (GC-MS). Based on the identification of intermediates, the degradation pathways and mechanism were proposed and discussed. Besides, the toxicity of the DBD treated 2,4-DCP solution was also assessed using GFP-expressing recombinant Escherichia coli (E. coli) as the testing organism, showing that plasma treatment could substantially reduce the toxic effect of 2,4-DCP.

Sonochemical degradation of triclosan in water in a multifrequency reactor.

Degradation of triclosan (TCS) by multifrequency ultrasound (US) was studied at high and low frequencies. Frequency effect on initial degradation rates was analyzed, and an optimum frequency was found. Power density always has a positive effect on degradation rates over the whole equipment work range. A reaction mechanism similar to that proposed by Serpone resulted in a pseudo-linear model that fitted statistically better than the nonlinear model proposed by Okitsu. Pulsed US showed a positive effect on degradation rates; however, simultaneous analysis of the effect of power, frequency, pulse time, and silent time did not show a clear trend for degradation as a function of pulse US variables. According to these results and those for degradation in the presence of radical scavengers, it was concluded that US TCS degradation was taking place in the bubble/liquid interface. A toxicity test was conducted by Microtox®, showing a decrease in toxicity as TCS concentration decreased and increase in toxicity after total depletion of TCS. Eight possible degradation by-products were identified by GC-MS analysis, and a degradation pathway was proposed.

Regioselectivity in Reactions between Bis(2-benzothiazolyl)ketone and Vinyl Grignard Reagents: C- versus O-alkylation-Part III.

The reaction between bis(2-benzothiazolyl)ketone and vinyl Grignard reagents bearing different substituents on the vinyl moiety gave the product derived from attack on the carbonylic carbon- and/or oxygen-atom. The regioselectivity of the attack depends on the kind of substituents bound to the vinylic carbon atoms and on their relative position. The reaction between vinylmagnesium bromide and 2-methyl-1-propenylmagnesium bromide was carried out under different experimental conditions and in the presence of radical scavengers. The results indicate a plausible mechanistic pathway involving radical intermediates in the case of O-alkylation, but a polar ones in the case of classic C-alkylation. This agrees with our previous reports indicating a key role played by the delocalization ability of the substituents bound to the carbonyl group in driving the regioselectivity of the vinylmagnesium bromide attack towards O-alkylation. Further support of this was obtained by diffractometric analysis of four distinct bis(heteroaryl)ketones.

Mechanistic insights into the biomimetic catalytic hydroxylation of arenes by a molecular Fe(NHC) complex

The mechanism of the hydroxylation of benzene by an iron(II) bis(NHC) complex, [FeII(NCCN)(CH3CN)2](PF6)2 (1; NCCN=bis(o-imidazol-2-ylidenepyridine)methane), in the presence of hydrogen peroxide was investigated. The invariance of the catalytic system towards the presence of radical scavengers and an inverse intermolecular kinetic isotope effect (KIE) allow to rule out a hydrogen abstraction pathway. Additionally, using 1,3,5-[D3]benzene as substrate, NIH-shift products were detected, resembling the reactivity of naturally occurring enzymes and some molecular biomimetic iron complexes. Supported by density functional theory calculations, the aromatic hydroxylation reaction is proposed to proceed via an iron-arene σ-complex as intermediate species.

Enhanced ozonation degradation of atrazine in the presence of nano-ZnO: Performance, kinetics and effects

Enhanced ozonation degradation of atrazine (ATZ) with nano-ZnO (nZnO) as catalyst and the influences of the operational parameters have been investigated through semi-continuous experiments in this study. The results demonstrated that the combination of ozone (O3) and nZnO showed an obvious synergetic effect and the ATZ degradation conformed to pseudo-first-order kinetics. An improvement of ATZ degradation efficiency by 41.8% and pseudo-first-order rate constant by more than a factor of four was obtained in the O3/nZnO process after 5min of reaction compared to O3 alone. Meanwhile, the degradation efficiency of ATZ was gradually enhanced with increasing nZnO dosage and initial pH in the range from 3.0 to 8.0, and a higher amount of ATZ was degraded when the initial concentration of ATZ rose from 0.5 to 5mg/L. Additionally, sulfate ion, chloride ion, nitrate ion and low concentrations of humic acid substances led to enhancement of the ATZ degradation. The notable decrease of ATZ removal efficiency observed in the presence of radical scavengers and the results of free radical tests indicated that OH is the dominant active radical species. The mechanism investigation demonstrated that the enhancement effect could be attributed to the introduction of nZnO, which could promote the utilization of O3, enhance the formation of superoxide radical, and further accelerate the production of hydrogen peroxide and the generation of OH/O2−.

Rapid degradation, mineralization and detoxification of pharmaceutically active compounds in aqueous solution during pulsed corona discharge treatment

In the present study, plasma generated by pulsed corona discharge was used for the degradation of diclofenac, carbamazepine and ciprofloxacin. Pollutants in aqueous solution were plasma treated under two categories: single and mixed pollutant condition. Mixed pollutant condition showed an antagonistic behaviour and thus the degradation time was higher for mixed condition compared to the single condition. At different voltage and frequencies, degradation efficiency followed the trend, diclofenac>carbamazepine>ciprofloxacin. Acidic pH slightly favoured the degradation process whereas in presence of radical scavengers (HCO3−, CO32– and humic acid) the degradation yield was significantly decreased. With an input power of 101.5 W, complete degradation was achieved within 4–16 min of plasma treatment for pharmaceutical's concentrations of 1–10 mg/L. As the pollutant concentration increased from 1 to 10 mg/L, the pseudo first order rate constant decreased, while yield increased. Complete degradation pathway of diclofenac, carbamazepine and ciprofloxacin in plasma treatment process are proposed by identifying the intermediates using LC-MS analysis. TOC analysis confirmed 80% mineralization within 10 min of plasma treatment for higher pharmaceutical's concentrations of 10 mg/L. The microalgae ecotoxicity study and disc diffusion test confirmed the complete detoxification of PACs that took place after 6 min of plasma treatment.

Advanced oxidation of preservative agents in H2O2/UVC system – Kinetics study, transformation products and toxicity assessment

Phenylphenol isomers (hydroxylated derivatives of biphenyl) are widely used as a preservative agents and disinfectants in many branches of industry.This work focuses on removal of phenylphenol isomers from aqueous solution using H2O2/UVC process. The influence of different operating variables such as pH, initial concentration of hydrogen peroxide, initial concentration of target compounds, fluence rate and presence of radical scavengers on degradation rate was investigated. Moreover, transformation products and toxicity of the reaction solutions were studied. The reaction rate constants of hydroxyl radicals with phenylphenol isomers were determined by using classical and competition kinetics. The value of reaction rate constant depends on the position of the hydroxyl group in the aromatic ring and follows the order: ortho- phenylphenol<meta- phenylphenol<para- phenylphenol. The main by-products of initial degradation steps were dihydroxybiphenyl isomers, phenol and isomers of 2,4-hexadienoic-6-oxo-6-phenyl acid or trihydroxybiphenyl. A properly selected degradation time led to mineralization of reaction solution, and after 2h of reaction the total organic carbon reduction was equaled to 89, 87 and 71% for ortho- phenylphenol, meta- phenylphenol and para- phenylphenol solution, respectively. The application of advanced oxidation in H2O2/UVC system led to achieving non-toxic reaction solutions.

Formation of N-Nitrosodimethylamine during Chloramination of Secondary and Tertiary Amines: Role of Molecular Oxygen and Radical Intermediates.

N-Nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduct from water chloramination. Despite the identification of numerous NDMA precursors, essential parts of the reaction mechanism such as the incorporation of molecular O2 are poorly understood. In laboratory model systems for the chloramination of secondary and tertiary amines, we investigated the kinetics of precursor disappearance and NDMA formation, quantified the stoichiometries of monochloramine (NH2Cl) and aqueous O2 consumption, derived 18O-kinetic isotope effects (18O-KIE) for the reactions of aqueous O2, and studied the impact of radical scavengers on NDMA formation. Although the molar NDMA yields from five N,N-dimethylamine-containing precursors varied between 1.4% and 90%, we observed the stoichiometric removal of one O2 per N,N-dimethylamine group of the precursor indicating that the oxygenation of N atoms did not determine the molar NDMA yield. Small 18O-KIEs between 1.0026 ± 0.0003 and 1.0092 ± 0.0009 found for all precursors as well as completely inhibited NDMA formation in the presence of radical scavengers (ABTS and trolox) imply that O2 reacted with radical species. Our study suggests that aminyl radicals from the oxidation of organic amines by NH2Cl and N-peroxyl radicals from the reaction of aminyl radicals with aqueous O2 are part of the NDMA formation mechanism.

Solar light-induced degradation of ethyl paraben with CuOx/BiVO4: Statistical evaluation of operating factors and transformation by-products

In this work, the solar light-induced photocatalytic degradation of ethyl paraben (EP) was studied using CuOx/BiVO4 with 0.75wt.% copper loading, a relatively new photocatalyst that can exploit a large portion of the solar spectrum. The synthesized catalyst had a primary crystallite size of ca 37nm, a specific surface area of 1m2/g and a direct bandgap of 2.3eV. A factorial design methodology was implemented to evaluate the importance of EP concentration (500–1500μg/L), catalyst concentration (100–500mg/L), reaction time (10–60min), the presence of radical scavengers (pure water or 500mg/L bicarbonates) and initial solution pH (3–9) on EP removal. All individual effects were statistically significant and so was the second-order interaction of EP concentration with reaction time. Interestingly and differently from the majority of photocatalytic studies, the presence of bicarbonates promotes the photocatalytic degradation of ethyl paraben. The photocatalytic activity drops from 98% to 79% after five consecutive runs, possibly due to accumulation of oxidation by-products. Liquid chromatography-time of flight mass spectrometry (LC-TOF-MS) revealed that EP degradation occurs mainly via dealkylation followed by hydroxylation reactions and the formation of methyl paraben, 4-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid and 3,4-dihydroxybenzoic acid as primary transformation by-products.

Decomposition of Iodinated Pharmaceuticals by UV-254 nm-assisted Advanced Oxidation Processes

Iodinated pharmaceuticals, thyroxine (a thyroid hormone) and diatrizoate (an iodinated X-ray contrast medium), are among the most prescribed active pharmaceutical ingredients. Both of them have been reported to potentially disrupt thyroid homeostasis even at very low concentrations. In this study, UV-254 nm-based photolysis and photochemical processes, i.e., UV only, UV/H2O2, and UV/S2O82−, were evaluated for the destruction of these two pharmaceuticals. Approximately 40% of 0.5μM thyroxine or diatrizoate was degraded through direct photolysis at UV fluence of 160mJcm−2, probably resulting from the photosensitive cleavage of C-I bonds. While the addition of H2O2 only accelerated the degradation efficiency to a low degree, the destruction rates of both chemicals were significantly enhanced in the UV/S2O82− system, suggesting the potential vulnerability of the iodinated chemicals toward UV/S2O82− treatment. Such efficient destruction also occurred in the presence of radical scavengers when biologically treated wastewater samples were used as reaction matrices. The effects of initial oxidant concentrations, solution pH, as well as the presence of natural organic matter (humic acid or fulvic acid) and alkalinity were also investigated in this study. These results provide insights for the removal of iodinated pharmaceuticals in water and/or wastewater using UV-based photochemical processes.

Sonochemical Synthesis, Characterization and Sonocatalytic Performance of Terbium-Doped CdS Nanoparticles

Terbium-doped cadmium sulfide nanoparticles with different terbium contents were successfully synthesized via sonochemical route. The prepared samples were characterized by X-ray diffraction, scanning electron microscopy, photoelectron X-ray spectroscopy, and UV–Vis diffuse reflectance spectroscopy techniques. The as-prepared nanocatalyst were used for sonocatalytic degradation of Methylene Blue. Among the different amounts of dopant, 8 % Tb-doped CdS showed the highest sonocatalytic activity. The order of inhibitory effect of radical scavengers was 1, 4 Benzoquinone > SO3 2− > CO2 3−> I−. The effects of various parameters such as initial dye concentration, catalyst loading, ultrasonic power, and the presence of radical scavengers were investigated.

Photoelectrocatalytic degradation of the antibiotic sulfamethoxazole using TiO2/Ti photoanode

Photoelectrocatalysis (PEC) of sulfamethoxazole (SMZ) was investigated using TiO2/Ti (UV-A) photoanode. Complete photoelectrocatalytic degradation of SMZ was achieved after 70min at 0.5V, while SMZ resisted to photolysis and electrolysis. Langmuir-Hinshelwood analysis yielded an adsorption constant (K) of 0.519L/mg for the studied PEC-TiO2 system, with K being 3–4 times of those from photocatalysis. PEC degradation of SMZ accelerated with increasing anodic potential (0–0.5V), declining pH (from 10.1 to 2.7), and increasing NaCl concentration (1–100mM). These trends were consistent with the understanding that higher potential gradient reduces recombination of holes and electrons, lower pH favors photoadsorption through modulation of SMZ speciation and TiO2 surface charge, and higher Cl− level encourages formation of chlorine radicals. Molar ratios of HO and chlorine radicals showed that the effects of pH and Cl− levels were coupled, with the level of PEC activity linked to the relative dominance of [Cl2−] over [HO]. In the presence of radical scavengers, SMZ photoelectrocatalysis was lowered by 30% at merely 10mg/L of humic acid, and was reduced to <5% of the original rate at 10% methanol. The inhibitory effect of humic acid and methanol on PEC was consistent with the view that HO and Cl2−/active chlorine species were the main oxidants in a Cl−-present environment. A 3-times above-average photocurrent was observed in 10% methanol, whose unusual photocurrent increase was attributed to sequential current doubling – additional electron flow due to reactive adsorbate-hole interaction – through a series of proposed reactions: conversion of hVB+-bound methanol through formaldehyde and formic acid to CO2. Implications of the findings with respect to practical application of PEC are presented.